Why do I get wrong result?

Question

I tried 10.05 +0.05
and it evaluated to 10.100000000000001!
Why can't I get 10.1 instead?
Can anyone tell me the reason please?
https://code.sololearn.com/cpwRdAu5ZLK9/?ref=app
https://code.sololearn.com/cpwRdAu5ZLK9/?ref=app

Answer 1

Because there's no exact representation of decimal numbers like 0.1, 0.2, 0.3 etc as binary number inside the computer.

you can even compare two float and double precision number with the same value and get an unexpected result just because the precision of approximated binary number

float f = 10.1f;
double d = 10.1;

if ( f == d)
// yes
else
// no

And guess what, you get no.
10.9999999999 or 10.1000000001
Vs.
10.9999999999999999998 or
10.1000000000000000001